Purification of benzene and homologues thereof



Oct. 4, 1949. H. J. HEP'P PURIFICATION OF BENZENE AND HOMOLOGUES THEREQF Filed Aug. l2, 1946 ATTORNEYS Patented Oct. 4, 1949 PURIFICATION 0F BENZENE AND HOMOLOGUES THEREOF Harold J. Hepp,

Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Application August 12, 19i6, Serial No. 689,872 5 Claims. (Cl. 26o-674) This invention relates to the purification of benzene and its lower alkyl homologues. More specifically it relates to a process for the removal of olens from benzene and its lower alkyl homologues.

Benzene and its lower alkyl homologues have long been products of commercial importance. The destructive distillation of coal has been and is a major source of such compounds. In more recent years, the cracking of petroleum has provided another source of these compounds, and the products of this operation at least much of the timecontain benzene and alkyl benzene compounds in recoverable amounts.

. Fractionation, with or without combination with such other, methods as absorption, is used as a means of recovery and separation of these compounds from the cracked products. Such methods, however, do not readily yield pure products. Oleiins, produced in large amounts by cracking of petroleum, are especially diftlcult to separate from aromatic compounds by such means, and, consequently, the aromatic compounds separated from mixtures of aromatics and n oleiins contain excessive amounts of oleflns for many uses.

Treatment with sulfuric acid has been practiced in removing the olefins from these mixtures, although such side reactions as sulfonation leave much to be desired in this method.

Solid aluminum chloride has alsoA been used as a. treating agent in removal of olefin impurities from benzene and its lower alkyl homologues with satisfactory removal of olefins, but this method results in excessive loss of desired aromatics.

In copending application Serial No. 635,590 led December 17, 1945, now issued as U. S. Patent 2,458,777, issued January 11, 1949, there is described a process whereby the olefinic content of an aromatic concentrate is removed by treatment with a fluid aluminum chloride-hydrocarbon complex. In this process, the olefin-containing aromatic concentrate is contacted with the uid aluminum chloride complex, preferably in a countercurrent, multistage system, the olens being polymerized and held by the aluminum chloride-hydrocarbon complex. Due to the high solubility of aromatics in the complex, the complex phase recovered from the process contains a high proportion of the desired product of the process,

to provide an improved and thiscomplex phase is decomposed withwater, and the oils contained in this phase arerecovered and combined with the product hydrocarbons prior to fractionation for separation into desired products.

In the process of the copending application above-identified, however, the aluminum chloride is lost as a water solution and the very high boiling oils of the catalyst are included in the product stream going to the fractionating zone. The principal object of the present invention ls process for the removal of olefins from benzene and its lower alkyl homologues. Another object is to provide such a lprocess wherein the aluminum chloride content of the aluminum chloride-hydrocarbon complex is maintained in av form such that it can be recovered. Another object is to provide a process of the foregoing type which is simple and economical. Numerous other objects will appear hereinafter.

According to the present invention, an olencontaining aromatic concentrate is contacted with a iiuid aluminum chloride-hydrocarbon complex, and the hydrocarbon phase is then separated from the complex phase. Ihe hydrocarbon phase is substantially olefin-free and contains a small amount of dissolved complex. The complex phase contains a relatively large proportion of dissolved aromatics, and is extracted with a predominantly paralnic and/or naphthenic hydrocarbon substantially free of oleflns and of such boiling range that it is easily separated by fractionation from the extracted aromatic compound. The two hydrocarbon streams are then substantially freed of dissolved and suspended catalyst, and the contained product is recovered by suitable means, such as fractionation. The complex phase, substantially freed of dissolved aromatic content, may then be processed for recovery oi' anhydrous aluminum chloride.

The uid aluminum chloride-hydrocarbon complex `used in this process may be one especially made up for use in this process, or it may be excess complex discarded from an alkylation or isomerization process. Suitable complexes will have a heat of hydrolysis between about 200 and about 480 calories per gram, preferably between 280 and 380 calories per gram. Details of methods of making these complexes are well known in the art and need not be discussed here. A typical complex may be made by mixing aluminum chloride and kerosene (preferably substantially free from olefins and aromatics) in the weight ratio of 5 to 8 and has a heat of hydrolysis of 323 calories per gram.

The solubility of the aromatic compounds in a complex discarded from an ethylene-isobutane alkylation system has been found to be more than one volume of aromatic compound per volume of original complex. Thus, the complex phase separating from the eiiluent of the zone in which the olefin-containing aromatic concentrate and aluminum chloride-hydrocarbon complex are contacted will contain a high proportion of physically dissolved aromatics. The dissolved aromatics will usually amount to from about 40 volume per cent to about 65 volume per cent of the total complex phase. The complex will also contain some oleiins held in the complex by chemical bonds. Extraction of the complex with a liquid paraiiinic and/or naphthenic hydrocarbon yields an extract phase of paraiiinic and/or naphthenic hydrocarbon and extracted aromatic, while the oienic content of the complex is not extracted. The oleiins are apparently present in the complex phase bound in some manner to the aluminum chloride and are thus not distributed between the hydrocarbon phase and complex phase when the extracting hydrocarbon is added. p

The aromatic hydrocarbons will physically dissolve some aluminum chloride-hydrocarbon `complex, though the solubility oi complex in the aromatic hydrocarbon is much smaller than the solubility of aromatic hydrocarbon in the complex. At room temperature, the treated aromatic hydrocarbons usually hold in solution less than about two volume per cent complex. A portion of the dissolved complex may be separated from the aromatic hydrocarbon phase by addition of parailinic and/or naphthenic hydrocarbons. It is preferable that the parailinic and/or naphthenic hydrocarbons are of such boiling range that the added hydrocarbon is readily separated from the desired aromatic product by fractionation.

The proportions of the complex and the oleilncontaining aromatic hydrocarbon may vary over wide limits.

drocarbon phase and a complex phase exist under the conditions of the contacting step. The amount of complex taken should be suilciently large to eilect complete or substantially complete removal of the olefin contained in the aromatic.

The proportions of the complex and the saturated hydrocarbon employed to extract the dissolved aromatic therefrom are preferably such that substantially all of the dissolved aromatic is extracted from the complex by the extractant hydrocarbon. In. this way, loss of aromatic is kept at a minimum.

One specific embodiment of this invention ln which olen-containing benzene is treated is shown in the accompanying drawing, and the following description of the process with reference to the drawing will give a better understanding of this invention. Numerous valves, pumps and controls have not been included in this schematic drawing, but these can readily be supplied by those skilled in the art.

Glenn-containing benzene from a source not shown is introduced through pipe I to the lower I often prefer to use such propor- 1 tions that two phases, namely an aromatic hypart of contactor II. Through pipe I2 a iluid aluminum chloride-hydrocarbon complex with a heat of hydrolysis within previously-described limits is introduced in the upper section of contactor I I. 'I'he contactor I l preferably is a packed tower or plate tower in which countercurrent flow of hydrocarbon and complex is maintained, intimate contacting of complex and hydrocarbons being facilitated by the packing or plates. The temperature in the contactor II may be from 40 F. to 250 F., preferably from 100 F. to 175 F., and the contactor is operated under suiiicient pressure that substantially liquid phase is maintained. Though not here shown, contacting may be accomplished by mechanically agitated contactors, preferably in a multistage countercurrent system such as described in previously mentioned application Serial No. 635,590.

The treated benzene containing dissolved complex and some suspended complex is withdrawn from tower II through pipe I3, cooler I3a being utilized to cool the eiliuent if desired, and, through a T, pentane from a source to be described is added through pipe 24. The velocity through pipe I3 is such that turbulent iiow is maintained and mixing of the pentane and benzene accomplished by this turbulence. The mixed pentane and benzene is conducted to settler I6, where the hydrocarbon and suspended complex separate to form an upper hydrocarbon phase containing a small amount of dissolved complex and a lower aluminum chloride-hydrocarbon complex phase containing dissolved hydrocarbon.

Substantially spent complex is removed from the bottom of the tower II through pipe I6, and complex accumulating in settler I4 is removed through pipe l5 and conducted to pipe I6. The combined stream then is conducted to stripper I1. If desired, a portion of this stream of complex and dissolved hydrocarbon may be recycled to the contactor II through pipe 28, pump 29, and pipe 30, and the remainder of the stream then conducted to stripper Il. The lower section of stripper I1, that below dotted line I8, functions as a countercurrent contacting section and may either be packed with a suitable packing material such as Raschig rings, Beryl saddles and numerous others, or may contain bubble cap trays or perforated trays. The upper section, that above 50 dotted line I8, contains no packing or trays and functions as a settling zone. Pentane is introduced into stripper I1 at the bottom through pipe 25 from a source to be described, and the rising stream of pentane strips aromatics from the 55 downowing complex. The pentane and aromatics rise into the settling zone of stripper I1, where any suspended complex drops back to the stripping zone.

The complex, stripped of at least a major por- 80 tion of its aromatic content, is removed from the `bottom of stripper I'I through pipe 3l and is conducted to an aluminum chloride recovery system, not here shown. Any of the numerous processes for recovery of aluminum chloride from its hydrocarbon complex may be used, but I prefer to use the method described and claimed in cepending application Serial No. 651,962 led March 4, 1946.

The hydrocarbon from stripper I1 is removed through pipe 20 and the hydrocarbon phase from settler I4 is removed through pipe I9. The two are admixed and the combined stream thence conducted to caustic and/or water washer 2i,

where any dissolved aluminum chloride and/orv dissolved and/or suspended aluminum chloridehydrocarbon complex is removed from the hydrocarbon. From washer 2 l the hydrocarbon is conducted'through pipe 22 to fractionator 23, where the pentane is taken overhead through pipe 24. A portion of the pentane is conducted through pipe along a path previously described into the bottom of stripper I1, and the remainder is carried by pipe 24 through another previously described path into admixture with the benzene stream in line I3. Makeup pentane may be added to pipe 25 through pipe 26.

Benzene and heavier are removed from fractionator 23 through pipe 21, thence to product fractionation, not shown, if purification is desired; or this stream may be conducted to storage if of suflicient purity for the use to which it is put.

It is preferred that the paraflinic and/or naphthenic hydrocarbon used to extract aromatics from the complex be lower boiling than the aromatic compound undergoing purification.

In some specific embodiments of this invention, however, it is possible to utilize a higher boiling extracting hydrocarbon. In either event the boiling point of the `extracting hydrocarbon should be sufhciently far removed from that of the aromatic hydrocarbon to be readily separated therefrom by ordinary fractional distillation.

Examples of saturated hydrocarbons which may be employed for the extraction of the' dissolved aromatic hydrocarbon from the liquid aluminum chloride-hydrocarbon complex are acyclic parains such as liquid propane, liquid butane (either normal or iso), normal pentane, isopentane, any of the hexanes, any of the heptanes, any of the octanes, cyclic parains such as cyclopentane, cyclohexane, methyl cyclopentane, methylcyclohexane, mixtures of any two or more of the foregoing suchas occur in the form of straight-run naphtha, kerosene, natural gasoline, etc., provided only that the boiling point be suihciently removed from benzene or other recovered aromatic to afford easy separation from the recovered aromatic.

The lextractant should be relatively free from olel'lns or other objectionable impurities such as diolens, acetylenes, sulfur, sulfur compounds, etc. In most cases it is undesirable to use an extractant which forms an azeotrope with the aromatic. Thus normal hexane, methylcyclopentane and cyclohexane are reported to form azeotropes of the minimum-boiling type with benzene and normally would not be employed as extractant hydrocarbons for benzene.

Pentane such as normal pentane or pentane or a mixture of normal pentane and isopentane is often preferred for carrying out the extraction step because pentane boils suiciently isog quired if propane or either of the butanes were I employed.

The aromatic hydrocarbon purified in accordance with the present invention is usually benzene; however instead of benzene. other lower alkyl homologues thereof may be puried. Examples are toluene, ethylbenzene, cumene and xylene. The invention is primarily applicable to monocyclic aromatic hydrocarbons selected from the group consisting of benzene and its lower alkyl homologues, that is compounds derivable from benzene by replacement of one or more nuclear hydrogen atoms with lower alkyl groups, i. e. those having from one to four carbon atoms including methyl, ethyl, n-propyl, isopropyl, n-butyl, secbutyl, isobutyl, tert-butyl.

Example Twenty-ve cc. of an aluminum chloridehydrocarbon complex discarded from an ethylene-isobutane alkylation system was saturated with benzene, the nal volume being 55.5 cc. The benzene-saturated complex was extracted with isopentane; 66.5 cc. of hydrocarbon phase and 37 cc. of complex phase were recovered. By refractive index analysis, the hydrocarbon phase was found to contain 34 volume per cent benzene.

The extracted complex phase was again extracted with a second cc. portion of isopentane, and 31 cc. of complex phase and 55.5 cc. of hydrocarbon phase were recovered. By refractive index analysis, the hydrocarbon phase was found to contain 12 volume per cent benzene.

The extracted benzene was calculated to be 29.2 cc., or a recovery of over 95 per cent of the benzene dissolved in the complex.

I claim:

l. A process for removing olefins from monocyclic aromatic hydrocarbons which comprises liquid-liquid extracting an olefin-containing monocyclic aromatic hydrocarbon with liquid aluminum chloride-hydrocarbon complex having a heat of hydrolysis of from 200V to 480 calories per gram to effect the removal of the olen from the aromatic hydrocarbon by said complex in the form of an olefin-containing aluminum chloride-hydrocarbon complex, a portion of said aromatic hydrocarbon dissolving in said aluminum chloride-hydrocarbon complex, withdrawing from the extracting step the resulting olefin-free aromatic hydrocarbon phase and the resulting complex phase, introducing saturated hydrocarbon selected from the group consisting of parains and naphthenes to said aromatic hydrocarbon phase and thereby precipitating entrained complex therefrom, liquidliquid extracting said complex phase with saturated hydrocarbon easily separable from the aromatic hydrocarbon and selected from the group consisting of parains and naphthenes,

withdrawing an extract phase of saturated hyrecovering aromatic hydrocarbon as a product of the process.

2. A process for removing olens from monocyclic aromatic hydrocarbons, which comprises liquid-liquid extracting the olefin-containing monocyclic aromatic hydrocarbon with sufficient quantity of a liquid aluminum chloride-hydrocarbon complex having a heat of hydrolysis of from 200 .to 480 calories per gram to remove all of the 7 l complex with a low-boiling paramn hydrocarbon to remove said portion of aromatic hydrocarbon from said complex phase, combiningthe aforesaid varomatic fraction and the portion of aromatic removed from said complex phase, caustic washing said combined aromatics removing all dissolved aluminum chloride complex, and recovering puried olen-free monocyclic aromatic hydrocarbons as a. product of the process.

' cient quantity of a liquid aluminum chloride-hy;

drocarbon complex having a heat of hydrolysis of from 200 to 480 calories per gram to effect the removal of all of the oleiin from the aromatic hydrocarbon by said complex, simultaneously dissolving a portion of aromatic in said complex, with drawing from the extracting step the resulting olen-free aromatic hydrocarbon phase and the resulting complex phase, introducing saturated hydrocarbon selected from the group consisting of low-boiling parailns and naphthenes to said aromatic hydrocarbon phase and thereby precipitating entrained complex therefrom, liquid-liquid extracting said complex phase with saturated hydrocarbon selected from the group consisting of low-boiling parailins and naphthenes and separable from the aromatic hydro- `carbon by ordinary fractional distillation and thereby effecting selective extraction of the aromatic hydrocarbon dissolved in said complex without extracting any olefin from said complex, withdrawing a thus separated extract phase oi low-boiling saturated hydrocarbon and aromatic hydrocarbon and a raflinate phase of extracted complex, caustic washing all of said separated aromatic hydrocarbon to remove any aluminum chloride or aluminum chloride-hydrocarbon complex dissolved or suspended therein, and fractionally distilling the resulting extract to sepa.- rate a fractionof said saturated hydrocarbon suitable for recycle to said second extracting step and to said precipitating step and a. fraction of oleiin-free aromatic hydrocarbon.

5. 'I'he process of removing oleiins from benzene which comprises liquid-liquid extracting the olefin-containing benzene with an aluminum 1 chloride-hydrocarbon complex having a heat o'f hydrolysis of from 280 to 380 calories per gram, said complex being present in suflicient quantity to remove all of said oleiins, the proportions of said benzene and said complex being such that two phases exist under the conditions of the y, extracting step, conducting said extracting step at a temperature ot from 100 to 175 F. and a precipitate, separating the thus precipitated complex and combining same with the complex resulting from said extracting step, countercurrent- 1y extracting in a second extracting step the resulting complex in liquid-liquid manner with liquid pentane and thereby eiecting selective extraction of substantially all of the benzene dissolved in said complex without extracting any olefin from said complex, withdrawing from the e second extracting step an extract phase consisting essentially of the pentane and the benzene and a railinate phase consisting. of extracted complex, washing said extract phase with an aqueous solution capable of removing any aluminum chloride or aluminum chloride-hydrocarbon complex contained therein, passing the resulting extract to a fractional distillation zone and there fractionally distilling same to separate same into an overhead fraction of pentane and a bottoms fraction of olefin-free benzene, and recycling said overhead fraction of pentane both to said step of admixing pentane with said benzene phase and to said step of extracting said complex phase with pentane.

HAROLD J. HEPP.

REFERENCES CITED The following references are of record in the 'file of this patent:

UNITED STATES PATENTS Number Name Date 2,257,086 Atwell Sept.- 30, 1941 2,260,279 dOuville et al. Oct 21, 1941 2,395,022 Sutton et al. Feb. 19, 1946 2,404,591 Naragon July 23, 1946 2,413,260 Soday Dec. 24, 1946 

